The invention relates to an arrangement in which the light emitted by a source of light is directed by means of an illumination optics onto a surface on which an image can be focussed that can be detected by means of a projection optics.
Examples of such arrangements are slide or film projectors in which, for purposes of attaining uniform illumination, a light bundle stemming from a light source is projected by means of a condenser onto a slide or film image that is then subsequently displayed on a screen with an objective as the projection optics.
In particular, however, the subject matter being addressed here is a recent technology in which deformable mirror matrices serve to generate video images. These deformable mirror matrices consist of an array of individual deformable mirrors that can assume two states, namely, zero and one, depending on the selected direction of reflection. The number of rows and columns of the array corresponds to the video standard for lines and pixels per line of the video image to be depicted. In order to also allow gray scale or colors on the part of individual pixels, the deformable mirrors associated thereto are pulse code modulated, depending on the pixel information, so as to rapidly switch these deformable mirrors back and forth between reflection in one of the two directions and reflection in the other direction, so that, on the average over time, the duty cycle between the states zero and one gives rise to a corresponding intermediate value between light and dark. Such deformable mirror matrices can be obtained, for instance, from Texas Instruments Incorporated.
As in the case of the known projectors mentioned above, the optics employed for such deformable mirror matrices consist of an illumination optics of the deformable mirror matrix and of a projection optics that is normally referred to as an objective, in order to project the image content onto a screen, a process in which both front and rear projection is possible.
The term screen as used here should be understood in its broadest sense. Especially for show applications, screen here also refers, for example, to the vapor of a smoke-making machine or to a wall of water.
Owing to space problems with the illumination, up until now, optics having a long focal length have been used as the illumination optics and as the projection optics, so that a certain size has always been necessary for these projectors with deformable mirrors. Moreover, due to the long light distances, loss of light is possible, which is why a greater input power is required and thus more heat also needs to be dissipated which, in turn, calls for a larger size. Consequently, with smaller projectors, and thus also with the demand for reduced heat generation, an image with large screen diagonals is not possible at all.
However, there is an avid interest in small and bright projectors. They should be easy to transport and capable of generating a sufficiently bright image of a suitable size under normal indoor lighting conditions. Efforts are already under way to replace the portable projectors that are just now coming onto the market by the next generation of considerably smaller projectors, the so-called palm-top projectors. Such projectors call for substantially smaller optics systems, both for the illumination optics and for the projection optics. It would be conceivable to try to achieve this through the miniaturization of the known optics, although the size of the light bulb, the heat problem and the resultant additional cooling means would always define a lower limit. Moreover, the deformable mirror matrices always have to be of a certain size in order to be able to reflect a sufficient amount of light.
A similar set of problems is also found when it comes to reflective LCD""s.
The objective of the invention is to provide a new arrangement for illumination and projection purposes which allows the construction of such miniaturized projectors.
This objective, which at first appeared to be unattainable in view of the above-mentioned requirements, is achieved on the basis of the above-referenced state of the art in that the illumination optics (first optics) has an optical means located beyond the source of light and a prism positioned between the surface and the optical means, whereby the light coming from the optical means is deflected without reflection by means of the prism. In this manner, the first optics, namely, the illumination optics, can be situated very close to the other optical elements of the projection optics (second optics) and, in the extreme case, parallel to the optical axis of the second optics. As a result, the compactness of the projector can be drastically increased, as will be elaborated upon in greater detail below with reference to embodiments. The essential aspect here is that the light incident upon the prism is only deflected by refraction.
Even greater compactness can be achieved according to another refinement in which the second optics is divided into a first and a second partial optics, whereby the first and second partial optics have a shared optical axis. The first optics contains the optical means and the second partial optics, so that the second partial optics is a component of the first partial optics as well as of the second partial optics. The incident light needed for the illumination stems from the optical means (third partial optics). In order to allow a projection, the light that comes from the third partial optics and that is incident upon the second partial optics includes an angle relative to the shared optical axis, whereby the third partial optics lies outside of an area that is traversed from the second to the first partial optics by the light that is reflected off the surface.
The fact that such a breakdown into a first, second and third partial optics is possible is, at first, unexpected since, in view of the prescribed long focal lengths, the current state of the art requires small apertures for the illumination of the deformable mirror matrix cited as an example as well as for depicting their image content; as experience has shown, this leads to the situation wherein the beam paths of the illumination light and of the reflected light then have to overlap. Due to the small aperture angles that are normally employed, it would fundamentally not be possible to use partial optics to uncouple the light path lengths of the light bundle that is incident upon the deformable mirror matrix from that of the light reflected by the deformable mirror matrix. Only now, with the arrangement according to the invention, has it become possible to realize partial optics having appropriately short focal lengths, as a result of which the useable apertures can be selected so as to be sufficently large, and a sufficiently large path can be kept free for the third partial optics, so that the light emerging from the deformable mirror matrix can pass through unhindered. The special configuration of such optics is known to the person skilled in the art.
This further development differs markedly from the familiar approaches for the miniaturization of known devices. In particular, it could have been expected that the person skilled in the art, after recognizing the heat problem associated with miniaturization, would have dedicated a great deal of her/his thoughts to designing a particularly space-saving cooling system.
A suitable cooling system, however, generally does not pose any problem with this arrangement, since the main heat-generating elements, namely, the deformable mirror matrix as well as the source of light, are located outside of the three partial optics. The back of these elements remains completely free, so that, in contrast to the known arrangements, no special attention needs to be paid to the space for the cooling means, a space that might have to be left free for optical elements. Consequently, a compact, efficient cooling system can be used for the deformable mirror matrix.
Unexpectedly, it has turned out that this arrangement also accounts for increased light intensity. This is due to the fact that, in view of the smaller focal lengths needed for illumination and for collecting the light that comes from the deformable mirror matrix and that is then to be projected, the distance from the deformable mirror matrix to the optics can be kept considerably smaller than in the case of the state of the art, so that less light is lost.
A prism can also be configured in such a way that light bundles of different colors are separated and, after this split, they are then directed onto different deformable mirror matrices on which differing color separations are focussed in order to depict color images. In comparison to other solutions, for instance, with a color wheel, this accounts for an overall greater light output relative to the electric power that has been fed in.
Owing to the underlying principle here, the third partial optics can be designed, for example, in such a way that a light source focussed onto a point is imaged again by this partial optics onto the point of the deformable mirror matrix cited as an example. However, it has turned out to be considerably simpler in terms of the uniformity of the image if the third partial optics is designed in a focussing manner, that is to say, if it converts a parallel beam into a point. Then, on the input side of the second partial optics, a parallel beam can be assumed that is subsequently focussed on the deformable mirror matrix for imaging purposes. Even though in this case, generally more space is needed for the third partial optics in order to guide the light to the input side of the second partial optics so as to generate the parallel light beam, this greatly increases the uniformity of the illumination. Then, there is no need for more space when the above-mentioned device is used for purposes of deflecting the beam path.
As already made clear above, the invention entails the special advantage that it allows the optimization of apertures for imaging and for illumination purposes. In particular, the following embodiments of the invention have proven to be especially advantageous, namely, those wherein the second partial optics on the side of the light source has an aperture greater than 0.3 and especially 0.5, and the third partial optics is designed for an illumination angle xcex8 on the surface which is configured so as to reflect behind the second partial optics with sin xcex8 smaller than 0.3 and especially smaller than 0.2. As the aperture increases, a smaller distance than is known from the state of the art becomes possible between the deformable mirror matrix cited as an example (reflecting surface) and the first or the second optics.
Due to this favorable aperture for the illumination, it is ensured in a simple manner that the light coming from the deformable mirror matrix can be projected by the illumination optics onto a screen without hindrance.
The above-mentioned features turn out to be particularly advantageous when the reflective surface is a rectangular imaging element, especially a deformable mirror matrix or a reflective LCD, and when the light bundle that is incident upon the third partial optics has a rectangular beam profile adapted to the aspect ratio of the light bundle.
The advantage of the use of the arrangement according to the invention with a deformable mirror matrix has already been elaborated upon above. In view of the fact that the light bundle has a rectangular beam profile adapted to the aspect ratio of the light bundle, the light used for the illumination can be transmitted almost in its entirety onto the deformable mirror matrix, as a result of which a maximum light intensity is generated on the image.
When it comes to deformable mirror matrices, it is likewise advantageous for the illumination to be as uniform as possible. In order to be able to save on optical components here, according to an advantageous embodiment of the invention, a mixing rod is provided in order to generate the rectangular beam profile before the third partial optics. A mixing rod mixes the light emitted by a light source by means of multiple reflections. For this purpose, it is possible to employ, for example, a cuboid rod with rectangular incident and emergent surfaces, whereby total reflection takes place multiple times as the light passes from the source of light to the surface area, so that the place on the base of the prism-shaped mixing rod, from which the light emerges, is practically independent of the place of incidence. This creates a uniformly illuminated rectangular field that is imaged onto the deformable mirror matrix.
In principle, this mixing rod, too, can be arranged either before or after the third partial optics. With an eye towards promoting a compact design, however, it has been proven to be extremely advantageous when the mixing rod is placed between the illumination means and the third partial optics.
When this deformable mirror matrix technology is used to depict color images and when only one single matrix is used, it is common practice to provide a color wheel. A color wheel of this type known from the state of the art is a circular disk whose circumference has several sectors having different color filters. In order to generate a color image, this color wheel is spun rapidly, as a result of which the light is filtered sequentially according to different colors.
The information content on the deformable mirror matrix is also synchronized with the appertaining colors of the individual color filters through which the light passes in order to illuminate the matrix. Owing to the persistence of vision and to the adjusted rotational speed of the color wheel, the differing colors are perceived simultaneously and the various color separations sequentially focussed on the deformable mirror matrix are perceived as a single colored video image.
According to an advantageous embodiment, however, a deviation is made from this construction in that, for purposes of depicting color images, a single deformable mirror matrix as well as a color wheel are provided, whereby the color wheel is designed as a surface area of a cylinder that is divided into sectors with filters having different colors and that covers the incident and/or emergent surfaces of the mixing rod. In this manner, a particularly compact arrangement is achieved since, owing to the cylindrical design in comparison to the known circular disk, only a single dimension perpendicular to the longitudinal extension of the mixing wheel is used for the color wheel. This will be elaborated upon in greater detail below with reference to the figures.
Normally, such optics according to the state of the art call for great adjustment efforts in order to coordinate the individual axes with each other. Here, however, according to a preferred embodiment of the invention, it has been found to be advantageous that the adjustability of the position and/or angularity of the deformable mirror matrix serves as an element for the alignment.
The possibility to correct the angle and the distance is sufficient in order to optimally set the direction of illumination as well as the passage of light through the first and second partial optics.
In another advantageous embodiment of the arrangement according to the invention, the optical means has a first optical axis and the second optics has a second optical axis that is perpendicular to the surface whereby, as seen in a top view and in a side view, the first optical axis, together with the second optical axis, includes an angle that lies between 0xc2x0 and 90xc2x0 in each case. Moreover, an incident surface of the prism facing the optical means is arranged in such a way that, as seen in the side view and in the top view, the first optical axis is not positioned perpendicular to the incident surface. With this embodiment, the optical means can be arranged laterally adjacent to and above the second optics so that a very compact arrangement is obtained. Furthermore, through the arrangement of the prism, the two optical axes can be skewed with respect to each other, thus resulting in great design freedom.
The arrangement according to the invention can be advantageously further developed in that the optical axis of the optical means runs parallel to the optical axis of the second optics. Consequently, the optical means can be placed directly above the second optics, with the result that the arrangement according to the invention acquires a very streamlined design.